Photoelectrophoretic imaging processes using bisazo pigments

ABSTRACT

Bisazo compounds are disclosed as are monochromatic and polychromatic electrophoretic imaging processes using these compounds. A typical member of this group is N,N&#39;&#39;-bis 1-(1&#39;&#39;naphthylazo)-2-hydroxy-8-naphthyl adipdiamide.

United States Patent v Jones et al.

[451 Apr. 25, 1972 54] PHOTOELECTROPHORETIC IMAGING PROCESSES USINGBISAZO PIGMENTS [73] Assignee: Xerox Corporation, Rochester, NY.

[22] Filed: Mar. 19, 1970 [21] App1.No.: 29,315

Related U.S. Application Data [62] Division of Ser. No. 613,294, Feb. 1,1967, Pat. No.

[52] U.S. C1 ..204/l8l,96/i.2,96/1.3

[5 1] Int. Cl. ..G03g 13/22 [58] Field ofSearch ..204/181; 96/1, 1.2,1.3

[56] References Cited UNITED STATES PATENTS 3,384,565 5/1968 Tulagin eta1 ..204/ l 8! 3,384,566 5/1968 Clark ..204/181 Primary Examiner-CharlesE. Van Horn I Attorney-Stanley Z. Cole and James J. Raiabate ABSTRACTBisazocompounds are disclosed as are monochromatic and poiychromaticelectrophoretic imaging processes using these compounds. A typicalmember of this group is'N,N'-bis 1-( 1'.naphthylazo)-2-hydroxy-8-naphthy1 adipdiamide.

11 Claims, 1 Drawing Figure Patented April 25, 1972 INVENTORS SANTOKH S,LABANA FREEMAN B. JONES,JR.

TTO/PNEVS PHOTOELECTROPHORETIC IMAGING PROCESSES USING BISAZO PIGMENTSThis is a division of application Ser. No. 613,294, filed in the UnitedStates Feb. 1, 1967, now US. Pat. No. 3,562,248.

This invention relates to new compositions and to their manufacture anduse. It is particularly directed to new pigments which are especiallyuseful as electrically photosensitive pigments in electrophoreticimaging systems.

Many pigments, both organic and inorganic, are known and used in theprior art. While the known pigments are generally useful, the individualpigments generally have different specific undesirable characteristics.Inorganic pigments, as a class, generally exhibit high resistance tolight, water, alcohol, and oils, but have poor dispersing properties.Organic pigments, while generally higher in cost and lower in resistanceto degrading influences, generally have dispersing and workingcharacteristics and color qualities superior to inorganic pigments. Agreat many organic pigments are known. The following pigments aretypical. Anthracene pigments are generally very resistive to theinfluence of light, heat, acids and alkalies, but they tend to bleed inalcohol and are expensive. Triphenylmethane dyestuffs have brilliant,clean colors, but are very unstable. They often bleed in water andalcohol and have low resistance to acids and alkalies. Indanthrenepigments lack brilliance and tinctorial strength, but are among the mostpermanent pigments known. Toluidine pigments have high light resistancebut only fair resistance to acids and alkalies. These pigments may bleedin oil. Rhodamine pigments have brilliant clean colors but generally lowresistance to degrading influences.

As is apparent from the above discussion, most pigments have bothdesirable and undesirable characteristics. Thus, there is a continuingneed for improved pigments having good resistance to degradation, gooddispersing characteristics and brilliant, clean colors.

There has been recently developed an electrophoretic imaging systemcapable of producing color images which has an especially acute need forpigments having both clean, pure colors, and electricalphotosensitivity. This .process is described in detail and claimed inco-pending applications Ser. Nos. 384,737, now [1.5. Pat. No. 3,384,565;384,681, now abandoned; and 384,680, now abandoned, all filed July 23,1964. In such an imaging system, various colored light absorbingparticles are suspended in a non-conductive liquid carrier. Thesuspension is placed between electrodes, subjected to a potentialdifference and exposed to an image. As these steps are completed,selective particle migration takes place in image configuration,providing a visible image at one or both of the electrodes. An essentialcomponent of the system is the suspended particles which must beintensely colored and electrically photosensitive and which apparentlyundergo a net change in charge polarity upon exposure to activatingelectromagnetic radiation, through interaction with one of theelectrodes. Where particles of a single color are used, single coloredimages will be produced conforming to conventional black-and-whitephotography. Images may be produced in color where mixtures of two ormore differently colored particles are used. Particles of each color aresensitive only to light of a specific wave-length or narrow range ofwave-length thus permitting color separation.

Pigments used in the imaging particles for this system must have bothintense pure colors and be highly photosensitive. The pigments of theprior art often lack the purity and brilliance of color, the high degreeof photosensitivity, and/or the preferred correlation between the peakspectral response and peak photosensitivity necessary for use in such asystem.

It is, therefore, an object of this invention to provide pigments whichsubstantially overcome the above-noted deficiencies.

It is another object of this invention to provide electrophoreticimaging processes which overcome the abovenoted deficiencies.

It is another object of this invention to provide new pigmented coatingand molding compositions.

It is another object of this invention to provide novel pigments havingsuperior resistance to thermal and chemical degradation.

It is still another object of this invention to provide pigments havingsuperior electrical photosensitive characteristics.

It is another object of this invention to provide a multi-color particlemix capable of producing improved color images by electrophoresis.

it is still another object of this invention to provide novelpolychromatic electrophoretic imaging systems.

The foregoing objects and others are accomplished in accordance withthis invention, basically, by providing novel compositions and novelprocesses using said compositions, the compositions having formulasselected from:

Wherein: Y R is selected from the group consisting of phenylene andlower alkylenes; and Q X and Y are each selected from the groupconsisting of phenyl and naphthyl.

Wherein:

R is selected from the group consisting of phenylene and loweralkylenes; and Z is selected from the group having the formula:

The compositions of the above general formulas belong to the class ofbisazo compounds. These are generally produced from amino compounds bythe process of diazotization and coupling. They are azo pigments derivedfrom couplers obtained by condensing 8-amino-2-naphthols with variousdicarboxylic acid chlorides.

The compositions of the above general formula have in general thecharacteristics of intense color and of substantial insolubility in thecommon organic solvents. These pigments may be dispersed in the usualpaint and ink vehicles without dissolving excessively.

Of the compositions within the general formulas listed above N,N-bis[l-( l'-naphthylazo)-2-hydroxy-8-naphthyl] adipdiamide, N,N-bis l-(l'-naphthylazo)-2-hydroxy-8- naphthyl succindiamide, the cyclicbis-amide of terephthalic acid and4,4'-bis(8-amino-2-hydroxy-l-naphthylazo)-diphenyl are preferred for usein electrophoretic imaging processes since they have especially purecolor and are most highly photosensitive. Since the shade or tone of thecompositions and their spectral and photosensitive response varyslightly depending upon the substituents used, intermediate values ofthese variables may be obtained by mixing several of the differentcompositions.

The following examples further define methods of making the compositionsof the present invention. Parts and percentages are by weight unlessotherwise indicated. The examples below should be considered toillustrate various preferred embodiments of methods of preparing thepigments of the present invention.

EXAMPLE I Precursors are first prepared which are then diazotized andcoupled to form thepigment.

About 10 mols l-amino-7-naphthol is dissolved with warming in a minimumamount of 5 normal hydrochloric acid. This solution is boiled with about5 percent by weight of activated charcoal for about 5 minutes andfiltered hot. The filtrate is cooled to room temperature and pH isadjusted to 2 by adding sodium acetate crystals. The reaction mixture isthen cooled to about C. and stirred. About 5 mols adipic acid chlorideis added drop-wise. After the addition is complete, the stirring iscontinued for 3 hours and the reaction mixture is allowed to warm up toroom temperature. The solid product is separated by filtration andpurified by recrystallization from ethanol. The product is N,N-bis(7-hydroxyl -naphthyl)-adipdiamide.

About 1 mol of l-naphthyl amine is dissolved in about 400 ml. of 3normal hydrochloric acid and cooled to about 0 C. About I molof sodiumnitrite (as a 20 percent solution in water) is added slowly withconstant stirring and maintained at a temperature below 7 C. This issolution A.

In a separate vessel about one-half mol of the coupler prepared in thesecond paragraph above (N,N'-bis( 7-hydroxyl-naphthyl)-adipdiamide) isdissolved in a mixture of about '500 ml. of pyridine and 450 ml. of a 10percent solution of sodium hydroxide and 50 grams of ice. This issolution B.

Solution A is slowly added to solution'B with vigorous stirring whilemaintaining the temperature of the mixture below 10C. When the additionis complete, the reaction mixture is warmed to about 60 C. The mixtureis then diluted with water and the pigment isolated by filtration anddried in a vacuum oven at about 75 C. for about 8 hours. The product isN,N'- bis[ l-( l -naphthyl azo)-2-hydroxy-8-naphthyl] adipdiamidc.

EXAMPLE ll The precursors which are to be diazotized and coupled toproduce the desired pigment are first prepared as follows.

About 30 grams of l-amino-2-naphthol is dissolved in a mixture of about30 ml. pyridine and 200 ml. toluene with warming to about 60 C. About 6grams of phosphorous trichloride in about ml. of toluene isadded slowlyand the mixture is refluxed for about 2 hours. Then, succinic acidchloride is added and reflex is continued for another 2 hours. Thereaction mixture is cooled and about 120 ml. of a 10 percent sodiumcarbonate solution is added to it. Pyridine and toluene are removed bysteam distillation and the solid product isolated by filtration. Theproduct is purified by crystallization from ethanol. This product isN,N'-bis(7- hydroxy-l-naphthyl) succindiamide.

In one vessel one equivalent (one-half mol) of the coupler preparedabove is dissolved in a mixture of about 500 ml. of pyridine and 400 ml.of a 10 percent solution of sodium hydroxide and 50 grams of ice. Thisis solution A,

ln a second vessel, one equivalent (1 mol) of l-naphthyl amine isdissolved in about 400 ml. of a 3 normal hydrochloric acid solution andthe solution is cooled to about 0 C. About 1 mol of sodium nitrate (as apercent solution in water) is added slowly with constant stirring whilethe temperature is maintained below 7 C. This is solution B.

Solution B is slowly added to solution A with vigorous stirring whilethe temperature of themixture is maintained below l0 C. When theaddition is complete, the reaction mixture is warmed to about 60 C. Themixture is diluted with water and pigment isolation by filtration anddried in a vacuum at about 75 C. for about 8 hours. This product isN,N'-bis [l-(l'- naphthyl azo)-2-hydroxy-8-naphthyl] succindiamide.

The compositions of this invention are useful as pigments for coloringpaints, varnishes, and other coating and molding compositions. For suchuses, the pigment must generally be in finely powdered form. Theparticles may be reduced to a fine powder, for instance, by dispersingthe material in a hydrocarbon liquid and ball milling for about 48hours. In addition to the specific uses listed above, it has been foundthat the compositions of this invention may be dispersed in othernatural and synthetic resins resulting in colored compositions suitablefor coating and molding processes. Any suitable carrier resin may beused. Typical resins include balsam resins, phenol resins, phenol resinsmodified with colophony and other resins of which colophony constitutesa major part, coumarone resins and indene resins and the substancescovered by the collective term synthetic lacquer resins" which includesprocessed natural substances, such as cellulose ether; polymers such aspolyvinylchlorides, polyvinylacetates, polyvinylacetals, polyvinylethers, polyacrylic and polymethacrylic esters, polystyrene andisobutylene; polycondensates, e.g., polyesters such as phthalate resins;alkyd resins, maleic acid resins, phenol formaldehyde resins, ureaformaldehyde resins, melamine formaldehyde condensates, ketone resins,xylene formaldehyde resins, polyactams and polyamides; epoxy resins;polyadducts, such as polyurethanes and any suitable mixtures orcopolymers thereof.

The compositions of this invention are further useful as pigments inpaper making processes when a brightly colored paper is desired.Pigments of this invention may also be dispersed in synthetic filamentforming materials useful in the production of synthetic textiles. Theelectrically photosensitive characteristics of these compounds, i.e.,their ability to hold an electrostatic charge inthe dark and dissipateit in the light, makes them also useful in various electrophotographicimaging processes.

.The compositions .of this invention have been found to be especiallyuseful in electrophoretic imaging systems of the sort discussed above.An exemplary electrophoretic imaging system is schematically shown inthe FIGURE. This system is suitable for both monochromatic andpolychromatic image formation.

Referring now to the FIGURE, there is seen a transparent electrodegenerally designated 1 which, in this exemplary instance, is made up ofa layer of optically transparent glass 2 overcoated with a thinoptically transparent layer 3 of tin oxide, commercially available underthe name NESA glass. This electrode will hereafter be referred to as theinjecting electrode." Coated on the surface of injecting electrode 1 isa thin layer 4 of finely divided photosensitive particles dispersed inan insulating carrier liquid. The term photosensitive, for the purposesof this application, refers to the properties of a particle which, onceattracted to the injecting electrode, will migrate away from it underthe influence of an applied electric field when it is exposed tosuitable actinic electromagnetic radiation. For a detailed theoreticalexplanation of the apparent mechanism of operation of the invention, seethe above mentioned co-pending applications Ser. Nos. 384,737; 384,681and 384,680, the disclosures of which are incorporated herein byreference. Liquid suspension 4 may also contain a sensitizer and/or abinder for the pigment particles which is at least partially soluble inthe suspending carrier liquid. Adjacent to the liquid suspension 4 is asecond electrode 5, hereafter called the blocking electrode," which isconnected to one side of the potential source 6 to a switch 7. Theopposite side of potential source 6 is connected to the injectingelectrode 1 so that when switch 7 is closed, an electric field isapplied across the liquid suspension 4 between electrodes 1 and 5. Animage projector made up of a light source 8, a transparency 9 and a lens10 is provided to expose the dispersion 4 to a light image of theoriginal transparency 9 to be reproduced. Electrode 5 is made in theform of a roller having a conductive central core 11 connected to thepotential source 6. The core is covered with a layer of a blockingelectrode material 12, which may be Baryta paper. The pigment suspensionis exposed to the image to be reproduced while a potential is appliedacross the blocking and injecting electrodes by closing switch 7. Roller5 is caused to roll across the top surface of injecting electrode 1 withswitch 7 closed during the period of image exposure. This light exposurecauses exposed pigment particles originally attracted to electrode 1 tomigrate through the liquid and adhere to the surface of the blockingelectrode, leaving behind a particulate image on the injecting electrodesurface which is a duplicate of the original transparency 9. Afterexposure, the relatively volatile carrier liquid evaporates off, leavingbehind the image. This particulate image may then be fixed in place as,for example, by placing a lamination over its top surface or by virtueof a-dissolved binder material in the carrier liquid such as paraffinwax or other suitable binder that comes out of solution as the carrierliquid evaporates. The carrier liquid itself may be molten paraffin waxor other suitable binder. In the alternative, the pigment imageremaining on the injecting electrode may be transferred to anothersurface and fixed thereon.

Any suitable insulating liquid may be used as the carrier for thepigment particles in the system. Typical carrier liquids are decane,dodecane, N-tetradecane, paraffin, beeswax or other thermoplasticmaterials, Sohio Odorless Solvent 3440, (a kerosene fraction availablefrom the Standard Oil Company of Ohio), an Isopar-G, (a long chainsaturated aliphatic hydrocarbon available from the Humble Oil Company ofNew Jersey). Good quality images have been produced with voltagesranging from about 300 to 7,000 volts in the apparatus of the figure.

In a monochromatic system, particles of a single color are dispersed inthe carrier liquid and exposed to a black-andwhite image. A single colorimage results, corresponding to conventional black-and-whitephotography. In a polychromatic system, the particles are selected sothat those of different colors respond to different wave-lengths in thevisible spectrum corresponding to their principal absorption bands.Also, the pigments should be selected so that their spectral responsecurves do not have substantial overlap, thus allowing for colorseparation and subtractive multi-color image formation. In a typicalpolychromatic system, the particle dispersion should include cyancolored particles sensitive mainly to red light, magenta particlessensitive mainly to green light and ye]- low particles sensitive mainlyto blue light. When mixed together in a carrier liquid, these particlesproduce a black appearing liquid. When one or more of the particles arecaused to migrate from base electrode 1 toward an upper electrode, theyleave behind particles which produce a color equivalent to the colorofthe impinging light. Thus, for example, red light exposure causes thecyan color pigment to migrate, leaving behind the magenta and yellowpigments which combine to produce red in the final image. In the samemanner, blue and green colors are reproduced by removal of yellow andmagenta, respectively. When white light impinges upon the mix, allpigments migrate, leaving behind the color of the white or transparentsubstrate. No exposure leaves behind all pigments which combine toproduce a black image. This is an ideal technique of subtractive colorimaging in that the particles are not only each composed of a singlecomponent, but in addition, they perform the dual functions of finalimage color and photosensitive medium.

It has been found that the compounds of the general formula given aboveare surprisingly effective when used in either a single or multi-colorelectrophoretic imaging system. Their good spectral response and highphotosensitivity result in dense, brilliant images.

Any suitable different colored photosensitive pigment particles havingthe desired spectral responses may be used with the pigments of thisinvention to form a particle mix in a carrier liquid for polychromaticimaging. From about 2 to about 10 percent pigment by weight in thissuspension have been found to produce good results.

All of the following examples are carried out in an apparatus of thegeneral type illustrated in the figure with the imaging mix 4 coated ona NESA glass substrate through which exposure is made. The NESA glasssurface is connected in series with a switch, a potential source, andthe conductive center of a roller having a coating of Baryta paper onits surface. The roller is approximately 2 inches in diameter and ismoved across the plate surface at about 4 centimeters per second. Theplate employed is roughly 4 inches square and is exposed with a lightintensity of about 1,500 foot candles as measured on the uncoated NESAglass surface. Unless otherwise indicated, about 7 percent by weight ofthe indicated pig- 1 ments in each example is suspended in SohioOdorless Solvent 3440, the magnitude of the applied potential is about2,500 volts. All pigments which have a relatively large particle size asreceived commercially or is made are ground in a ball mill EXAMPLE IIIAbout 7 parts of N,N-di[ l-(l-naphthylazo)-2-hydroxy-8- naphthyl]succindiamide is suspended in about parts Sohio Odorless Solvent 3440.

The mixture is coated onto the injecting electrode and a negativepotential is imposed on the blocking electrode. The plate is exposedthrough a Wratten 29 filter and the neutral density stop wedge filter,thus exposing the plate to red light. The results are tabulated in TableI, below. This test is then repeated with a Wratten 61, a Wratten 47band no filter, thus exposing the plate to green, blue and white light,respectively. See Table I for results.

EXAMPLE IV A suspension is prepared as in Example III, except that herethe pigment is the cyclic bis-amide of succinic acid and 4,4- bis(8-amino-2-hydroxyl -naphthylazo)-diphenyl methane.

The response of this suspension to red, green, blue and white light isthen measured with a negative potential on the roller electrode. SeeTable I for results.

EXAMPLE V EXAMPLE VI A suspension is prepared by dispersing about 8parts N,N- bis l-( l -naphthylazo)-2-hydroxy-8-naphthyl] adipdiamide inabout I00 parts Sohio Odorless Solvent 3440.

The response of this suspension to red, green, blue and white light isthen measured with a negative potential on the roller electrode. SeeTable I for results.

EXAMPLE VII The tests of Example VI are repeated with a positivepotential on the roller electrode. Results are tabulated in Table I.

' EXAMPLE VIII A suspension is prepared by mixing about 7 parts thecyclic bis-amide of terephthalic acid and 4,4'-bis(8-amino-2-hydroxy-l-naphthylazo)-diphenyl in about I parts SohioOdorless Solvent 3440.

The response of this pigment to red, green, blueand white light ismeasured as in Example III. A positive potential is maintained on theroller electrode. See Table Ifor results.

Gamma, as listed in column six, is a standard photographic termreferring to the slope of the above mentioned curve and indicates imagedensity. The maximum and minimum reflection density produced are listedin columns seven and eight, respectively.

In each of the examples IX-XI below, a suspension including equalamounts of three different color pigments is made up by dispersing thepigments in finely divided form in Sohio Odorless Solvent 3440 so thatthe pigments constitute about 8 percent by weight of the mixture. Thismixture may be referred to as a tri-mix." These mixtures areindividually tested by coating them on a NESA glass and exposing them asin Example I above, except that a multi-color Kodachrome" transparencyis interposed between the light source and the plate instead of theneutral density and Wratten filters. Thus, a multi-color image isprojected onto the plate as the roller moves across the surface of thecoated piece of glass substrate. A Baryta paper blocking electrode isemployed and the roller is held at a negative potential of about 2,500volts with respect to the substrate. The roller is passed over thesubstrate six times, being cleaned after each pass. The potentialapplication and exposure are both continued during the entire period ofthe six passes by the roller. After completion of the six passes, thequality of the image left on the substrate is evaluated as to densityand color separation.

EXAMPLE IX The tri-mix comprises a cyan pigment, Monolite Fast Blue GS,the alpha-form of metal-free phthalocyanine, available from the ArnoldHoffman Company; a yellow pigment, Algol Yellow GC, C.I. No. 67300,l,2,5,6-di(C,C-diphenyl)- thiazole-anthraquinone, available from GeneralDyestuffs; and a magenta pigment, N,N-bis[l-(l'-naphthylazo)-2-hydroxy-8-naphthyl] succindiamide, prepared as described above. About 8parts of this tri-mix is suspended in about l00 Rollvr Wratten Examplepotential filter Gamma nx. Durin- Ill 2, 500 2.) O. 95 0. 8 0. 2

2, 500 None 0. 95 0. 8 0. 2

2, 500 (ll 3. (i 1. 8 0. 4

2,500 Noun White... 125 3. 0 1.8 0.4

V +2, 500 20 Rod 250 5. 0 2. 8 0. 1

+2,500 til Union... 125 5.0 3,8 0.1

+2.,500 Noni: White... 1'35 6. 0 2.3 0.1

.,500 47h Blue 1,000 1.25 1.3 0.4

\II +1500 2'.) Rod 00 1.4 1.4 0. 1

+12, 500 lil (1t'0tli 200 1.4 1. 4 0.05

+2, 500 Nonu 500 1. 4 1. 4 0. 05

+1500 None 150 0.3 0. 4 0.01

The electrophoretic sensitivity of the various pigments to red, green,blue and white light is tested according to conventional photographicmethods and the results are recorded in Table 1, above. In the table,the first column lists the-number of the test example. The second columngives a positive or negative electrical potential applied to the rollerelectrode in volts. The Wratten filters used in each example between thelight source and the NESA plate are listed in column three. The fourthcolumn lists the color of the light which is permitted to fall on theNESA plate. The fifth column gives the photographic speed of thephotosensitive mix in foot candles. The photographic speed is the resultof a curve of optical density plotted against the logarithim of exposurein foot candles.

parts of Sohio Odorless Solvent 34.40 andexposed to a full colororiginal as described above. A full color image of good qualityconforming to the original is produced on the injecting electrodesurface.

EXAMPLE X The tri-mix comprises a cyan pigment, Cyan GTNF, the beta formof copper phthalocyanine, C.l. No. 74160. available from the CollwayColor Company, a yellow pigment. l\'-2"-naphthylazo)-2-hydroxy-8-naphthyl] adipdiamide, prepared as describedabove. About 8 parts of this tri-mix is dispersed in about 100' partslsopar-G. This suspension is exposed to a natural color original asdescribed above. A full color image is produced on the injectingelectrode of good quality.

EXAMPLE XI The tri-mix comprises a magenta pigment, Watchung Red B, C.l.No. 15865, l-(4'-methyl-5'-chloroazobenzene-2-sullo fonicacid)-2-hydroxy3-naphthoic acid, available from E1. duPont de Nemours &Company; a yellow pigment,8,13-dioxodinaphtho-(2,l-b;2',3'd)-furan-6-carbox-(3-cyano-5- methoxy)anilide, prepared as described in copending application Ser. No.421,377, filed Dec. 28, [964, now US. Pat. No. 3,448,029 and a cyanpigment the cyclic bis-amide of terephthalic acid 7 and4,4'-bis(S-amino-Z-hydroxy-lnaphthylazo)-diphenyl prepared as describedabove. A suspension is formed and exposed to a full color original asdescribed above. A full color image, conforming to the original isproduced on the injecting electrode. 7

Although specific components and proportions have been described in theabove examples relating to methods of preparing the pigments of thisinvention and to methods of using these pigments in coating and moldingcompositions and in electrophoretic imaging systems, other suitablematerials as listed above, may be used with similar results. inaddition, other materials may be added to the pigment compositions tosynergize, enhance, or otherwise modify their properties. For 0 example,the pigment compositions of this invention may be electrically or dyesensitized, if desired, or may be mixed or otherwise combined with otherphotosensitive materials, both organic and inorganic.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is: I

l. The method of electrophoretic imaging comprising sub- 40 jecting alayer of a suspension to an applied electric field between at least apair of electrodes, at least one of which is at least partiallytransparent, and exposing said suspension to an image through saidtransparent electrode with activating electromagnetic radiation wherebyan image made up of migrated particles is formed on at least one of saidelectrodes; said suspension comprising a plurality of finely dividedparticles of at least one color, the particles of one color comprising aphotosensitive pigment having a general formula selected from the groupconsisting of:

(A) H O 0 H N ll R ti N wherein:

R is selected from the group consisting of phenyl and lower alkylradicals; and X and Y are each selected from the group consisting ofphenyl, naphthyl, lower alkyl substituted phenyl and lower alkylsubstituted naphthyl radicals H O (I) H N JLR E N N=NZN=N- O H Hwherein:

R is selected from the group consisting of phenyl and lower alkylradicals; and Z is selected from the group having the general formula:

ment is:

0 o s .t t s f s 5. The method of claim 1 wherein said photosensitivepigment is 6. The method of claim 1 wherein one of said electrodes is ablocking electrode.

7. The method of electrophoretic imaging comprising subjecting a layerof a suspension to an applied electric field between a pair ofelectrodes, at least one of which is at least partially transparent,said suspension comprising a plurality of finely-divided particles of atleast two different colors in a carrier liquid, the particles of eachcolor comprising a photosensitive pigment whose principal lightabsorption band substan- 5 tially coincides with its principalphotosensitive response band, simultaneously exposing said suspension toa pol \'chromatic light image through said partially transparentelectrode and then separating said electrodes whereby a polychromaticmigrated particle image is formed on the surface of at least one of saidelectrodes; the particles of one color comprising compositions havinggeneral formulas selected from the group consisting of:

W H 0 a H N ll R N N=NX Y-N=N d o H H wherein:

R is selected from the group consisting of phenyl and lower alkylradicals; and X and Y are each selected from the group consisting ofphenyl, naphthyl, lower alkyl substituted phenyl and lower alkylsubstituted naphthyl radicals (B) H O O H N ll R li N -N= -Z-N=N- O O HH wherein:

R is selected from the group consisting of phenyl and lower alkylradicals; and Z is selected from the group having the general formula:

l HO

ll. The method of claim 7 wherein said photosensitive pigment is

2. The method of claim 1 wherein said photosensitive pigment isN,N''-bis (1-(1''-naphthylazo)-2-hydroxy-8-naphthyl) adipdiamide.
 3. Themethod of claim 1 wherein said photosensitive pigment is N,N''-bis(1-(1''-naphthylazo)-2-hydroxy-8-naphthyl) succindiamide.
 4. The methodof claim 1 wherein said phOtosensitive pigment is:
 5. The method ofclaim 1 wherein said photosensitive pigment is
 6. The method of claim 1wherein one of said electrodes is a blocking electrode.
 7. The method ofelectrophoretic imaging comprising subjecting a layer of a suspension toan applied electric field between a pair of electrodes, at least one ofwhich is at least partially transparent, said suspension comprising aplurality of finely-divided particles of at least two different colorsin a carrier liquid, the particles of each color comprising aphotosensitive pigment whose principal light absorption bandsubstantially coincides with its principal photosensitive response band,simultaneously exposing said suspension to a polychromatic light imagethrough said partially transparent electrode and then separating saidelectrodes whereby a polychromatic migrated particle image is formed onthe surface of at least one of said electrodes; the particles of onecolor comprising compositions having general formulas selected from thegroup consisting of:
 8. The method of claim 7 wherein saidphotosensitive pigment is N,N''-bis(1-(1''-naphthylazo)-2-hydroxy-8-naphthyl) adipdiamide.
 9. The method ofclaim 7 wherein said photosensitive pigment is N,N''-bis(1-(1''-naphthylazo)-2-hydroxy-8-naphthyl) succindiamide.
 10. The methodof claim 7 wherein said photosensitive pigment is
 11. The method ofclaim 7 wherein said photosensitive pigment is